Same, Same But Different; Why Same Blood Pressure Readings May Mean Different Things

Internal Medicine Doctor

Internal Medicine Doctor

As an internal medicine doctor with clinical interests in hypertension and cardiovascular risk management, I have many patients who come to me to have a better understanding of blood pressure, and to find ways to better manage the condition.

It’s important to recognize that hypertension is a silent killer that requires careful monitoring. While it rarely causes direct symptoms, over time, high blood pressure will damage blood vessels and thus cause end-organ damage. This results in increased cardiovascular and cerebrovascular morbidity and mortality. Lowering blood pressure to target levels will reduce the risk of these diseases considerably.

In Singapore, the general recommendation remains to keep blood pressure below 140/90 mm Hg, with even lower target values for certain high-risk groups. In consequence, internal medicine doctors offering hypertension specialist services receive many referrals for the evaluation of people who exceed these values. On detailed assessment, however, many patients are not hypertensive at all, but are rather victim to a technical detail inherent in our oscillometric blood pressure measurement.

When we measure blood pressure, we typically do so at the upper arm. We measure flow oscillations in the blood streams, which the algorithms of the monitors translate into pressure values expressed as mm Hg. Historically, and before Riva-Rocci and Korotkoff learned to interpret these oscillations, measurement was done by tonometry, and the “mm Hg” expressed the distance a column of quicksilver was moved by the pulse, typically at the radial artery. The oscillations, however, are a compound reading of both flow and pressure, and these may differ between individuals, even when the final reading is the same.

The root cause of this is best explained by the concept of the Windkessel function of the large arteries. Large arteries contain elastin, which during diastole returns the arteries shape to the residual, lower diameter and thus maintains residual blood flow. The flow and pressure curves registered more peripherally add up, giving a relatively high systolic reading.

Elastin, however, degenerates with aging, so that the arteries become stiffer and pose greater resistance to the blood. In consequence, the pulse wave curve is pressure dominant in older individuals. If measured at the radial artery, the pulse waves will look similar, and the BP monitor will give an equally high reading for both young and old individuals.

While the Windkessel explanation is lately being replaced by more complex wave analytics that examine the effect of wave augmentation at the point of measurement, the resulting effect is the same: in individuals with high peripheral resistance, elevated peripheral blood pressure is more likely to signify hypertension compared to those with more elastic arteries.

In fact, there is an age group- late teens to early thirties – where the elasticity is relatively so dominant, that the systolic blood pressure appears to be elevated compared to diastolic blood pressure, while later in life, systolic and diastolic blood pressure slowly rise in parallel again, until the rise of diastolic blood pressure slows in older age. Such individuals do not have hypertension despite elevated systolic blood pressure readings, and do not benefit from antihypertensive treatment.

If the constellation is such that only the systolic blood pressure exceeds the target level of 140 mm Hg, while the diastolic blood pressure remains below 90 mm Hg, the invidividual, by definition, suffers from “Isolated Systolic Hypertension (ISH)”.

Isolated systolic hypertension (ISH) is the most common form of hypertension in older persons and its predictive value for adverse outcome is well known.

ISH, however, can be frequently found also in young individuals, especially among men, but its prognostic significance in this setting is still controversial. According to some authors, ISH in youth is a totally benign condition that can be called “spurious hypertension”, a phenomenon due to enhanced pulse pressure amplification of the pulse wave from central to peripheral sites. According to others, the main determinant of ISH in young individuals is increased sympathetic activity and the consequent hyperkinetic state characterized by elevated heart rate and stroke volume. This phenomenon is often amplified by a powerful alarm reaction to the medical visit – commonly known as the “white coat hypertension”.

Pulse wave analysis and non-invasive determination of central blood pressure can help to identify those with pulse pressure amplification. If the central blood pressure is within normal limits, the patient is well, and does not suffer from hypertension. Treatment is not necessary, and the individual should not be labelled as hypertensive as that may lead to exclusions if health insurance is applied for.

Book Appointment Call Us Today

Those individuals with increased sympathetic activity should be considered for treatment if the ISH shows high grade 1 or grade 2 hypertensive values, and the frequently associated overweight cannot be reduced by lifestyle optimization. If such patients show low peripheral resistance either by means of pulse wave analusis or other techniques such as bioimpedance cardiograph, the pharmacological approach should address the underlying condition i.e. a beta blocker (BB) should be used as first choice. If other classes of antihypertensives such as ACE-inhibitors (ACE-is), aldosterone receptor-blocks (ARBs) or calcium channel blockers (CCBs) are used, the resulting reduction in peripheral resistance may indeed lower blood pressure. This, however, often goes along with reflex tachycardia, thus enhancing the overall hyperkinetic state. The patient is likely to feel unwell and may show low compliance. Use of a beta-blocker will avoid this an lead to better overall compliance and effective blood pressure reduction. In the occasional male patient experiencing erectile dysfunction while on standard BB, a switch to nebivolol may lead to restitution of erectile function.

In patients with increased peripheral vascular resistance, who are also likely to be older, ACE-is, ARBs or CCBs would be drugs of first choice, and treatment should likely be started earlier. In line with our understanding of hypertension as one part of a spectrum of modifiable risk factors for vascular end-organ damage, the physician should also address other possible contributors to vascular damage: smoking, hyperlipidaemia and hyperuricaemia.

So while two individuals may have the same blood pressure measurements, the underlying conditions may vary considerably, and customized treatment based on assessment of the vascular status is likely to improve treatment compliance and success.

In conclusion, hypertension is a significant health issue that requires the expertise of an internal medicine doctor to manage effectively. By carefully monitoring blood pressure and differentiating between true hypertension and technical errors in measurement, an internal medicine doctor can reduce the risk of cardiovascular and cerebrovascular morbidity and mortality in their patients.

Book Appointment Call Us Today

About Dr Adrian Mondry

Dr Adrian Mondry is a Hypertension Specialist accredited by the German Hypertension League in Singapore. He was previously a senior consultant in the department of medicine at the National University Hospital and Ng Teng Fong General Hospital (NTFGH), Dr Mondry has more than 30 years of experience in the field of internal medicine.

Dr Adrian Mondry is recognised for his leadership and contributions in establishing the dedicated hypertension clinic within the National University Health System and fast-track deep vein thrombosis service at NTFGH.

Dr Adrian Mondry is fluent in English, German and French.

About Kaizen Medical

Kaizen Medical is located at Mount Elizabeth Novena Specialist Centre, Suite 11-57.

At Kaizen, we provide in depth health care to patients with multi-organs diseases; tackling undifferentiated presentations that cannot be easily assigned to a single organ.

Comments are disabled.